Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited’s midweek edition for 8-9 January 2008 By Arnie Coro Radio amateur CO2KK
Hi amigos radioaficionados around the world and orbiting Planet Earth… welcome to the mid week edition of Dxers Unlimited. I am Arnaldo, Arnie, Coro, radio amateur CO2KK and as always it’s my pleasure to be able to share with you all about seventeen minutes of on the air and on the web time,as well as having the opportunity to make the scripts available for reading via several e-mail specialized short wave listening and amateur radio distribution lists… Among the lists that distribute Dxers Unlimited’s scripts are the ODXA, Ontario DX Association, the Regenerative Receivers list, as well as the HCDX list…where you can read the scripts of the program usually on the same day that it goes on the air… Now here is item one… It’s about the use of one of the classic audio output tetrode vacuum tubes in another role, in this case as a regenerative detector, something that the 6V6 does with amazing performance according to experiments done by several homebrewers , including yours truly amigos..
Amazing as it may sound... the 6V6 metal cased tube is an excellent choice for a regenerative detector, with the glass version a still very good second choice.
Using screen grid regeneration control in a Hartley ( cathode tap ) type of detector , a 6V6 will provide not only very good detection of signals up to around 10 megaHertz , but also is absolutely absent from microphonics effects that are so annoying.
One pending experiment here at my workshop is to test the miniature type tube that is supposedly an exact equivalent to the 6V6, the type 6AQ5, just to see if the results achieved are identical to the excellent performance of the 6V6.
Another still pending experiment is to use a 6AG7 ( or Soviet equivalent
6P9 ) in the same Hartley type regenerative detector and compare results both as regards to sensitivity and smoothness of regeneration control.
Using the 6V6 in a regenerative receiver will reduce the tube types to just two in a very simple radio, as the second 6V6 ( metal or GT type ) will perform as the audio output stage... A better radio will require another tube ( maybe a dual triode or an audio pentode ) as the audio driver, and in the interest of perfection, one should add a RF amplifier stage ahead of the regenerative detector, just to properly isolate the detector from the antenna. The line up of such a four tubes 1940's decade prototype could then be 6SK7 RF amp, 6V6 detector, 6SJ7 audio pre-amp 6V6 audio output stage, and in true GLOWBUGS vacuum tubes fashion a 5Y3-G or GT , or a 6X5 dual diode rectifier... Operating the power supply at around + 150 volts DC , with regulated output also at +75 from a VR tube, will complete the receiver in full compliance with the 1940's technology...
BUT, you could maybe improve the design a little bit , by using 1N4007's in place of the 5Y3-G or GT, Zener diodes for the + 50 to +75 volts for the screen voltage supply to the regenerative detector, and also include a well regulated 6.0 volts power supply using solid state devices to feed the filaments of the 6V6 detector in the first place, and if you have enough current available, also use DC for the filament of the 6SJ7 audio preamplifier stage.
BTW, the 6SJ7-6V6 audio amplifier design I use here comes from the original Collins 75A1 receiver, also a " Classic" by its own account..
Si amigos, yes my friends , oui mes amis… the 6V6 classic audio output pentode offers excellent performance as a regenerative detector, and if you have never experimented with this particular type of radio receiver, my advice is to try as soon as possible, as you will be absolutely amazed with the performance achieved by this unique circuit… Item two, coming up in just a few seconds, after a short break for station ID… I am Arnie Coro your host here at the mid week edition of Dxers Unlimited… …… You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and here we attempt to cover all aspects of this wonderful hobby you and I enjoy so much: RADIO… Now item two: Emergency communications are perhaps the main reason why valuable spectrum space is allocated to the amateur radio service… and ham radio operators around the world continue to provide much needed emergency links when other telecommunictions systems fail for one reason or the other… It may be that everyone wants to use the cellphone and that brings the system down, or in the case of wired telephone services, the bad weather or an earthquake causes severe damages to the cables and exchanges… The amateur radio stations can be deployed immediately , and using a car battery for power are able to provide very effective links . Among the most interesting ways ham radio operators communicate during emergencies, the one known as NVIS or Near Vertical Incidence Skywave is able to provide short distance links within a range of between 10 and 500 kilometers around each of the stations, that can be operated at rather low power and with very simple antenna systems.
The development of simple, yet effective NVIS antenna systems for emergency communications systems continues to attract the attention of the more advanced amateur radio operators that are capable of using sophisticated antenna modeling software. But the final word about how effective a so called "cloud warmer" or more properly Near Vertical Incidence Radiator is working only comes after extensive tests and evaluations that will favor one antenna over another. Just recently at the ANTENNEX Webzine e-mail list a very interesting discussion about NVIS antennas for emergency communications was in progress, and as a result two very interesting new small sized, yet highly efficient antennas for NVIS operations were designed and will now be subjected to extensive testing. Both antennas are shorter than a half wave dipole, use coaxial cable feedlines and show a very reasonable bandwidth on the segment of 40 meters where the designers decided to place the antenna’s optimum performance area. One of the antennas uses a single mast or support structure that is only about 20 feet or 6 meters high, and the other antenna requires two supports or masts , also in the 20 feet or 6 meters high figure. These types of antennas have to be easily deployed by even a single station operator, and they should be ready for field installation packed into a very easy to unpack emergency station module.
As soon as I complete here the tests of the first of these antennas, I will make the results available during a special edition of Dxers Unlimited, and then also as a dot pdf document that can be sent via e-mail to Dxers Unlimited’s listeners around the world that may want to try it out also… As I said a while earlier, each and every amateur radio operator should have her or his station ready to cope with any possible emergencies, and to do so, having a highly efficient antenna for the type of communications mode that you foresee using is extremely important. A very experienced Cuban radio amateur operator who has participated during many hurricane emergency nets is always emphasizing to newcomers to the nets that emergency antennas should always be ready to be deployed and that one must practice how to install them, because when the real emergency comes it’s no time to start to find out how to install the antenna, and of course that your emergency station’s module, must be complete with spares and a minimum set of tools so that you can do field repairs whenever they are required. NVIS antennas can be used on the 160, 80, 60 and 40 meters bands, but typically they are used most frequently on 80 meters during the local evening hours and 40 meters during daytime… …….
This is Dxers Unlimited’s mid week edition amigos… and here is item three of the program… our most popular section of the show… la numero uno… You have questions and Arnie answers them… today’s question was sent by several listeners that are interested in getting their amateur radio stations ready to be able to handle emergencies… The questions came from New York, Vermont, Kansas and California, as well as from Alabama and Florida. They all want to know more about how to organize a portable station that can be quickly deployed in case an emergency situation requires the help of the radio amateurs of the community.
Well amigos, in the first place I will recommend having always ready to go a 2 meters band 5 Watt output handie talkie, a set of spare batteries , a battery charger capable of fast recharging and if possible also of providing a slower charging rate, and last but not least , two portable antennas. Please notice that I mention two portable antennas, because during an emergency situation, you will have no time to fix a broken antenna, so you must always include in the emergency station’s module, a second antenna as well as at least two lengths of coaxial cable with the adequate connectors . Then add, a pair of water bottles, hand tools, an LED flashlight and batteries for it, and a first aid kit… If one of the two antennas is an easy to assembly 4 or 5 element YAGI, it is much better than if the two antennas are of the omnidirectional type, because a YAGI BEAM ANTENNA can improve your signal a lot, without requiring more power to be drawn from your batteries. Whenever possible, try to include also a small solar panel too, so that you can recharge the hand held FM 2 meter transceiver batteries using solar energy…In an upcoming edition of the program I will provide information on the HF emergency station requirements and why it is also very important to keep it ready too… And now as always at the end of the show, here is Arnie Coro’s Dxers Unlimited HF propagation update and forecast… Solar activity is once again is expected to be between low and very low for the next several days of this week… solar flux is now near 80 units, and the A index was at a rather high 16 on Monday due to the effects of a high speed solar wind. No sporadic E events expected to occur in the Northern Hemisphere, but good chances of nice E skip openings do appear to be possible South of the Equator. Best bands for daytime short wave broadcast listening are the 25, 19 and 16 meter bands, and nightime reception will be best on 49 and 31 meters , with 25 meters also good on North to South propagation paths. See you all at the weekend edition of the program amigos, and don’t forget to send your comments about the show, radio hobby questions and QSL requests to arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro , Radio Havana Cuba, Havana, Cuba.
